[PATCH 00/63] Fix CONFIG_DRM_USE_DYNAMIC_DEBUG=y

[Louis Chauvet]

Le 20/02/2025 à 10:45, Simona Vetter a écrit :
> On Thu, Feb 20, 2025 at 09:31:41AM +0100, Greg KH wrote:
>> On Fri, Jan 24, 2025 at 11:45:14PM -0700, Jim Cromie wrote:
>>> This series fixes dynamic-debug's support for DRM debug-categories.
>>> Classmaps-v1 evaded full review, and got committed in 2 chunks:
>>>
>>>    b7b4eebdba7b..6ea3bf466ac6	# core dyndbg changes
>>>    0406faf25fb1..ee7d633f2dfb	# drm adoption
>>>
>>> DRM-CI found a regression during init with drm.debug=<initval>; the
>>> static-keys under the drm-dbgs in drm.ko got enabled, but those in
>>> drivers & helpers did not.
>>>
>>> Root Problem:
>>>
>>> DECLARE_DYNDBG_CLASSMAP violated a K&R rule "define once, refer
>>> afterwards".  Replace it with DYNDBG_CLASSMAP_DEFINE (invoked once in
>>> drm-core) and DYNDBG_CLASSMAP_USE (invoked repeatedly, in drivers &
>>> helpers).
>>>
>>> _DEFINE exports the classmap it creates (in drm.ko), other modules
>>> _USE the classmap.  The _USE adds a record ref'g the _DEFINEd (&
>>> exported) classmap, in a 2nd __dyndbg_class_users section.
>>>
>>> So now at modprobe, dyndbg scans the new section after the 1st
>>> __dyndbg_class_maps section, follows the linkage to the _DEFINEr
>>> module, finds the (optional) kernel-param controlling the classmap,
>>> examines its drm.debug=<initval>, and applies it to the module being
>>> initialized.
>>>
>>> To recapitulate the multi-module problem wo DRM involvement, Add:
>>>
>>> A. tools/testing/selftests/dynamic_debug/*
>>>
>>> This alters pr_debugs in the test-modules, counts the results and
>>> checks them against expectations.  It uses this formula to test most
>>> of the control grammar, including the new class keyword.
>>>
>>> B. test_dynamic_debug_submod.ko
>>>
>>> This alters the test-module to build both parent & _submod ko's, with
>>> _DEFINE and _USE inside #if/#else blocks.  This recap's DRM's 2 module
>>> failure scenario, allowing A to exersize several cases.
>>>
>>> The #if/#else puts the 2 macro uses together for clarity, and gives
>>> the 2 modules identical sets of debugs.
>>>
>>> Recent DRM-CI tests are here:
>>>    https://patchwork.freedesktop.org/series/139147/
>>>
>>> Previous rev:
>>>    https://lore.kernel.org/lkml/20240716185806.1572048-1-jim.cromie@gmail.com/
>>>
>>> Noteworthy Additions:
>>>
>>> 1- drop class "protection" special case, per JBaron's preference.
>>>     only current use is marked BROKEN so nobody to affect.
>>>     now framed as policy-choice:
>>>     #define ddebug_client_module_protects_classes() false
>>>     subsystems wanting protection can change this.
>>>
>>> 2- compile-time arg-tests in DYNDBG_CLASSMAP_DEFINE
>>>     implement several required constraints, and fail obviously.
>>>
>>> 3- modprobe time check of conflicting class-id reservations
>>>     only affects 2+classmaps users.
>>>     compile-time solution not apparent.
>>>
>>> 4- dyndbg can now cause modprobe to fail.
>>>     needed to catch 3.
>>>     maybe some loose ends here on failure.
>>>
>>> 5- refactor & rename ddebug_attach_*module_classes
>>>     reduce repetetive boilerplate on 2 types: maps, users.
>>>     rework mostly brought forward in patchset to reduce churn
>>>     TBD: maybe squash more.
>>>
>>> Several recent trybot submissions (against drm-tip) have been passing
>>> CI.BAT, and failing one or few CI.IGT tests randomly; re-tests do not
>>> reliably repeat the failures.
>>>
>>> its also at github.com:jimc/linux.git
>>>    dd-fix-9[st]-ontip  &  dd-fix-9-13
>>>
>>> Ive been running it on my desktop w/o issues.
>>>
>>> The drivers/gpu/drm patches are RFC, I think there might be a single
>>> place to call DRM_CLASSMAP_USE(drm_dedbug_classes) to replace the
>>> sprinkling of _USEs in drivers and helpers.  IIRC, I tried adding a
>>> _DEFINE into drm_drv.c, that didn't do it, so I punted for now.
>>>
>>> I think the dyndbg core additions are ready for review and merging
>>> into a (next-next) test/integration tree.
>>
>> So whose tree should this go through?
> 
> I'm trying to get some drm folks to review/test this, but thus far not
> much success :-/ I think it's good stuff, but I'm somewhat hesitant if no

I tested the VKMS driver with this, and it works!

Tested-by: Louis Chauvet <louis.chauvet at bootlin.com>

> one else agrees that it's useful for CI or in-field crash-recording or
> whatever ...
> 
> I guess worst case we can land it and hope it attracts more folks?
> 
> Wrt tree I don't care, but I guess we should then also land the drm side
> too.
> -Sima
> 
>> And I think the last patch in this series isn't correct, it looks like a
>> 000 email somehow.
>>
>> thanks,
>>
>> greg k-h
> 

-- 
Louis Chauvet, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com